An optical path network that supports current backbone networks mainly includes optical communication apparatuses such as wavelength multiplexing transmission apparatuses, optical add/drop apparatuses and optical cross connect apparatuses, transmission routes such as optical fibers connecting the apparatuses, and paths such as wavelengths connecting between optical communication apparatuses by passing through transmission routes. Especially, research and development of a transparent type optical path network is attracting attention, in which the transparent type optical path network is for connecting between optical communication apparatuses of the optical path network from an end to the other end without regenerative relay processing for the optical signal. One of problems for the transparent type optical path network is to determine a route on the network and to determine a wavelength to be assigned on the determined route when receiving a traffic transfer request. These are generally referred to as Routing and Wavelength Assignment (RWA) problem.
A conventional RWA scheme in the transparent type optical path network is described. As shown in FIG. 1, when performing RWA, a route is determined first by routing processing in general. The shortest path algorithm is often used for determining the route. As shown in FIG. 2, as the shortest path algorithm, there are a fewest-hop method, a shortest distance method and the like. The fewest-hop method is a method for minimizing the number of hops between end points of the route, and the shortest distance method is a method for minimizing the physical distance. After determining the route by these methods, a wavelength is assigned by a first-fit method, a most-used method, or the like. In the first-fit method, in a case where there are a plurality of candidates of wavelengths that can be assigned when selecting a wavelength on a route, wavelengths, to which numbers are assigned, are assigned in order from lower number. As to the numbers assigned to wavelengths, wavelengths are numbered in order from the shortest wavelength. Also, wavelengths may be numbered in order from the longest wavelength. In the most-used method, in a case where there are a plurality of candidates of wavelengths when selecting a wavelength on a route, the number of wavelengths used in the whole network is counted for each wavelength, and the most used wavelength is used preferentially (refer to non-patent document 1, for example).
The above-mentioned RWA method is expected to realize economy and power saving of the optical path network by efficiently utilizing limited wavelength resources in the transparent type optical path network.
In addition, recently, an optical network (band variable optical network) for flexibly assigning optical frequency resources is being studied. In a conventional transparent type optical path network, frequency resources are assigned based on fixed frequency bandwidths for the optical path. On the other hand, in the above-mentioned optical network, the network is configured by band variable transponders and band variable cross-connects, in which frequency resources are managed by more segmentalized slots (grids), and frequency resources only as needed are assigned in bands and routes of the optical path, so as to utilize resources efficiently.
By the way, as to terms representing communication resources used in the following explanation, “wavelength” is mainly used in explanation on a path in which the frequency bandwidth is fixed, and “frequency” is mainly used in explanation on a path in which frequency bandwidth is variable.